Radiant energy source



Nov. 16, 1965 G. P. PLOETZ 3,218,509

RADIANT ENERGY SOURCE Filed OC'b. 9, 1962 3 Sheets-Sheet 1 \C/MEd/V Aw new Pum INVENTOR. 650/96: P. P445722 6- P. PLOETZ RADIANT ENERGY SOURCE Nov. 16, 1965 3 Sheets-Sheet 2 Filed Oct. 9, 1962 INVENTOR. 650E625 R PAETZ Nov. 16, 1965 ca. P. PLOE TZ RADIANT ENERGY SOURCE 3 Sheets-Sheet 3 Filed Oct. 9, 1962 INVENTOR GEORGE F? PLO 7'2 United States Patent 3,218,509 RADTANT ENERGY SOURCE George P. liloetz, Concord, Mass, assignor to the United States of America as represented by the Secretary of the Air Force Filed Oct. 9, 1962, Ser. No. 229,509

12 Claims. ((11. 315111) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to a thermal and light radiation scarce, and more particularly to a primary high intensity thermal and light radiation source including electrodes, said electrodes being isolated in a chamber and then heated to a predetermined temperature by a secondary thermal source positioned outside of said chamber prior to initiating a plasma discharge in the region of said electrodes.

Modern image furnaces employ the air-blown highintensity carbon arc as a source of intense thermal radiation. This radiation is collected and focused by a pair of concave mirrors at a second position which is free from the contaminating environment of the arc. Prior to adaptation for image furnace use, the high-current or high-intensity carbon arc and the air-blown modification were developed and improved as illumination sources for searchlights and motion picture projectors. Although the air-blown carbon arc provides the most intense thermal radiation, thereby achieving the highest temperatures, it has the inherent drawback of unsteady operation and lack of smooth, easy control. One type of thermal and light imager known as the clam shell utilizes a highintensity blown carbon arc as the thermal radiation source. Full capability of this mirror arrangement is not achieved owing to the thermal radiation shadow losses caused by the negative carbon and fume exhaust scoop. Thus, there is a need for a high-intensity thermal radiation source for application to the clam shell type thermal and light imager.

Limitations to the air-blown carbon are are the rapid consumption of the positive electrodes, and the instabilities produced by a magnetic field, if utilized. In reference to the rapid consumption, 2 to 5 minute operation per electrode has been indicated, duration depending on the intensity desired. Magazine loading and automatic operation of a non air-blown are have been attempted. In spite of the automatic feed and positioning equipment, the radiation intensity directly observed as rapid fluctuations in the arc current varied considerably. For this reason, the conclusion was drawn that the air-burning carbon arc is an unsatisfactory source for the clam shell thermal and light imager.

A further limitation in the utilization of a carbon arc as a thermal source for image furnaces resides in the formation of smoke, carbon black deposits and/or opaque films which severely inhibit the transfer of the generated thermal energy. The smoke, carbon deposits and/ or opaque films are caused by striking the are which partially consumes the carbon electrodes of said arc. This contamination further increases during the lifetime of the arc.

The present invention provides a method and apparatus whereby the aforesaid rapid consumption of electrodes is prevented; the rapid fluctuations in intensity (both thermal and light radiation) are eliminated; and the smoke, carbon deposits, and/ or opaque films become non-existent.

In accordance with an embodiment of the present invention, primary and secondary sources of thermal energy are provided and interposed therebetween is a thermal and light imager. The primary thermal source is comprised of a multiplicity of electrodes enclosed in a vacuum chamber having a window, preferably of quartz or other transparent but high temperature resistant material. The secondary thermal source may be a conventional carbon arc which when energized transfers thermal energy to the electrodes of the primary thermal source by way of the interposed thermal and light imager. The temperatures attainable by this method and apparatus at the electrodes of the primary thermal source is very substantial and in the order of 3000 to 3500 C. When the electrodes of the primary source reach a high temperature, thermionic emission is provided therefrom. Thereupon an alternating voltage is applied between the electrodes of said primary source which in turn operates to cause a plasma discharge between the tips of the electrodes. It is to be noted that this plasma discharge is confined to the immediate vicinity of said tips. Upon the occurrence of above-described plasma discharge, the secondary thermal source may be removed and the combination of the primary thermal source and thermal imager may then be utilized as a thermal image furnace. The aforementioned combination may also be utilized as a source of high intensity light.

It is to be noted that the aforementioned secondary thermal source was described as a conventional carbon arc and was operated in combination with a thermal imager. However, the present invention is not limited thereto; for example, a secondary thermal source may be provided by way of induction heating wherein conventional induction heating apparatus is positioned outside of the above described vacuum chamber. The induction heating apparatus is then utilized to heat the electrodes enclosed in said vacuum chamber until thermionic emission is provided therefrom. Thereafter, an alternating current is applied to said electrodes until a plasma discharge occurs therebetween. At this time, the induction heating ceases and the electrodes enclosed in said vacuum serves as a primary thermal source capable of producing temperatures above 4200 C.

In the operation of the present invention, the secondary thermal source positioned outside of the chamber enclosing the electrodes permits the isolation of the electrodes in a contamination-free area, thereby eliminating any additional element therein tending to inhibit the transfer of thermal energy.

It is to be emphasized that the chamber enclosing the electrodes was described in terms of a vacuum. In place of a vacuum, the chamber may be under partial pressure supplied by way of introducing an inert gas therein.

It is therefor an object of this invention to provide a thermal and light radiation source for image furnaces which produce no fumes or deposits which would shadow the radiation.

It is another object of this invention to provide a thermal and light radiation source which offers improved stability inasmuch as it has silent operation without flickermg.

It is still another object of this invention to provide a thermal and light radiation source which offers longer periods of use between readjusting the electrodes and re placing them.

These and other objects, features and advantages of the present invention will be further apparent from the following detailed description thereof, particularly when read with reference to the accompanying drawings, in which:

FIG. 1 shows an assembly view in elevation partly in cross section of one embodiment of the invention, including a thermal and light imager and a primary and secondary source of thermal and light energy;

FIG. 2 shows a front view of the primary thermal and light radiation source including a vacuum pump and wiring diagram for three-phase AC. power; and

FIG. 3 shows a cross sectional view taken at 3-3 of FIG. 2.

Now referring in detail to FIG. 1, there is shown thermal and light imager 11 which is comprised of parabolic reflectors 11 and 12. Reflector 11 faces and abuts reflector 12 and they are joined together at their associated rims 13 by any suitable means such as cementing. Each of the reflectors has a focal length F. Parabolic reflectors 11 and 12 have overlaying focal lines such that the focal point of reflector 12 is at position 14 and that of reflector 11 at position 15. Positions 14 and 15 are at the vertex of their respective reflectors and are along the Z axis at the center of the reflectors. Parabolic reflectors 11 and 12 are also apertured at their respective vertices with the identical diameter d. Supporting members 15 and 17 are afiixed to reflectors 11 and 12, respectively, and are utilized to support thermal imager 10.

Secondary thermal source 18 is a carbon arc which is conventional and is mounted on supporting member 17 and so positioned that the tips of the electrodes thereof are located at position 15 (the focal point of reflector 11).

Primary thermal source 19 is mounted on supporting member 16 and so positioned that thermal energy generated thereby is at the focal point of reflector 12, which is located at position 14.

Primary thermal radiation source 19, as shown in FIG. 1, 2, and 3 includes spherical vacuum chamber 21 comprised of two hemispheres, one of which is a highly polished reflecting surface 22 in housing 23 in which there are openings 24, 25, and 26to provide insertion of carbon rod holders 4!), 41, and 4-2 respectively, symmetrically spaced each 120 away from the other, and an opening 51 for attachment to passageway 52 which in turn connects to vacuum pump 53. The other hemisphere is dome 54- made of quartz which is transparent to heat and light radiation and is attached to door 55 with O ring 56 to insure air-tight connection. Door 55 is attached to hinge assembly 57 to allow opening and closing and is secured to housing 23 by latch assembly 58 with O ring 52 between door 55 and housing 23 to insure air-tight connection.

Electrodes 27, 28, and 29, made of carbon rods, are provided with assemblies 59, 6t), and 61, respectively. Each of the assemblies are identical and a cross section of a single carbon rod assembly is illustrated in FIG. 3

which is now referred to in detail.

Electrode 27 is retained by holder 40 made of conducting material to which in turn electrical connections are made. The end portion of electrode 27 is fluted to allow air to escape from receiving hole of holder 49 during periods of evacuating chamber 21. Holder 42 is secured by shaft 32 which is secured to stud 36 by knurled gland nut 35 that is tightened to stud 36 which is concentric with opening 24. A knurled gland nut 35 is tightened, pressure is placed upon 0 ring 37 located between nut 35 and stud 36 and surrounding shaft 32 and this pressure upon shaft 32 holds it secure to stud 36 which in turn is attached to housing 23 and is made air tight by O ring 39. Carbon rod holder is made secure to insulated shaft 32 by knurled gland nut 38 being tightened to shaft 32 which is threaded at the outer end, thereby causing pressure upon 0 ring 39 which in turn places pressure upon carbon rod holder 40 thereby securing it to shaft 32.

Hence electrode 27 can be positioned in two ways, by adjusting the holder 40 in shaft 32 and also by adjusting shaft 32 in stud 36.

Three phase alternating current is used as an electrical source as shown in FIG. 2 by connecting carbon rod holders 4t), 41, and 4-2 to variacs 43, 44, and by way of their associated variable connectors, 46, 4'7, and 48 respectively. If desired connectors 4s, 47, and 48 may be mechanically interconnected to provide simultaneous variation thereof.

Terminals 8t), 81, and 82 of variacs 43, 44, and 45 respectively provide connection to three phase source of A.C. power 83 by way of fuses 87, S8, and 89 respectively, and by way of triple pole, single throw switch 84. Variaces 43, 44, and 45 are interconnected at point 35 which is then grounded.

The are of secondary thermal source 18 mounted on supporting member 17 is positioned to be at the focal point 15 and the arc of primary thermal source 19 mounted on supporting member 16 is positioned to be at focal point 14. Radiation from secondary thermal source 13 is directed to reflector 11 and is then reflected therefrom in a manner such that only parallel radiation strikes parabolic reflector 12 which in turn converges the radiation at its focal point 14 which is also the apertured vertex of parabolic reflector 11 at which position the tips of electrodes 27, 23, and 29 of primary thermal source 19 are placed.

Primary thermal source 19 operates in a vacuum caused by vacuum pump 53 joined to vacuum chamber 21 by passageway 52. Electrodes 2'7, 28, and 2% made of carbon rods are positioned so they are in close proximity to each other. The positioning of any electrode can be accomplished either by adjusting electrode holder 31 in insulated shaft 32 or by adjusting insulating shaft 32 in stud 36.

The tips of electrodes 27, 28, and 29 are heated by secondary source 18 to approximately 30003500 C. which causes thermionic emission therefrom. Three phase alternating voltage is then applied between heated electrodes 2'7, 23, and 29 by closing switch 34 and then varying variac 43, 44, and 45. As a result the temperature is gradually raised to 40004200 C. due to thermionic emission current. Carbon vapor is caused to be generated and carbon plasma discharge is formed between hot electrodes 2'7, 28, and 25. The carbon evaporated becomes ionized and takes on a positive charge which causes it to transfer to the cathode where it solidifies. Using alternating voltage between electrodes 27, 23, and 29 causes the direction of flow of positive carbon ions to alternate which averages out material displacement, thereby preventing undue consumption. The plasma even though contained in vacuum chamber 21 is restricted to the immediate vicinity of hot electrodes 27, 22, and 29 and no material escapes to dome 54'; as smoke or evaporated film deposit which would shadow its radiation.

Since material loss is very slow, the life of electrodes 2'7, 28, and 22 is materially and substantially extended.

Although the use of carbon is highly desirable because of its high sublimation point, other electrode material can be used such as tungsten.

By operating in a vacuum, the burning of electrodes 27, 28, and 22 is eliminated and heat losses due to conduction are reduced. The same result is obtained using partial presusre of inert gas.

After the plasma discharge is obtained, secondary thermal source 18, together with thermal and light imager 10, can be removed making available primary thermal source 19 as a source of heat and light radiation. Or if only secondary thermal source 18 is removed, it leaves thermal and light imager 10 to direct radiation from primary thermal source 19.

What is claimed is:

1. A high intensity radiant energy system comprising a primary arc source of radiant energy consisting of a multiplicity of electrodes in a vacuum chamber, a secondary thermal source of radiant energy, means interposed therebetween to transfer said radiant energy from said secondary thermal source to said primary source to provide thermionic emission in said primary arc source and means to apply alternating current to said multiplicity of electrodes upon said occurrence of said thermionic emission to provide a plasma discharge between said multiplicity of electrodes.

2. A high intensity radiant energy system according to claim 1. wherein said electrodes are carbon.

3. A high intensity radiant energy system according to claim 1 wherein said multiplicity of electrodes consists of three electrodes being connected to a three-phase A.C. voltage source.

4. A high intensity radiant energy system according to claim 1 wherein primary arc source comprises a chamber containing inert gas.

5. A high intensity thermal and light system as described in claim 1 wherein said evacuated chamber is in the form of a sphere and is comprised of a pair of hemispheres, one of said pairs having a highly reflective interior surface and the other of said pair being formed of quartz.

6. A high intensity radiant energy system comprising a primary arc source of radiant energy consisting of a multiplicity of electrodes in a vacuum chamber, a secondary thermal source of radiant energy, means interposed therebetween for transferring said radiant energy from said secondary thermal source to said primary thermal source to provide thermionic emision in said primary arc source, said transferring means including a first and second radiant energy parabolic reflector facing and abutting each other and having the focus of each reflector at the vertex of the other, and means for applying alternating current to said multiplicity of electrodes upon occurrence of said thermionic emission to provide a plasma discharge between asid multiplicity of electrodes.

7. A high intensity radiant energy system according to claim 6 wherein said electrodes are carbon.

8. A high intensity radiant energy system according to claim 6 wherein said multiplicity of electrodes consists of three electrodes connected to a three-phase A.C. voltage source.

9. A high intensity radiant energy system according to claim 6 wherein primary arc source comprises a chamber containing inert gas.

10. A high intensity thermal and light system comprising a primary thermal and light source having a multiplicity of arc electrodes isolated in an evacuated chamber, a secondary thermal source positioned outside of said chamber, means interposed between said primary and secondary thermal sources to focus thermal radiation from said secondary source upon said arc electrodes of said primary source to heat said are electrodes to provide thermionic emission therefrom, said focusing means including a first and second radiant energy parabolic reflector facing and abutting each other and having the focus of each reflector at the vertex of the other, and means to apply an alternating voltage to said arc electrodes of said primary source upon said thermionic emission to provide a plasma discharge therefrom.

11. A high intensity thermal and light system comprising a primary thermal and light source having a multiplicity of arc electrodes isolated in an evacuated chamber, a secondary thermal source positioned outside of said chamber, means interposed between said primary and said secondary sources to focus thermal energy from said secondary source upon said arc electrodes of said primary source to attain a predetermined temperature thereof, said focusing means including a first and secondary radiant energy parabolic reflector facing and abutting each other and having the focus of each reflector at the vertex of the other, and means to initiate a plasma discharge confined to immediate vicinity of said are electrodes of said primary source upon attaining said predetermined temperature.

12. A high intensity thermal and light source consisting of a multiplicity of arc electrodes isolated in an evacuated chamber, said chamber being in the form of a sphere and including a pair of hemispheres, one of the pair having a highly reflective interior surface and the other of said pair being formed of quartz.

References Cited by the Examiner UNITED STATES PATENTS 1,804,049 5/1931 Claus 313- 1,901,128 3/1933 Smith 3l3-200 2,543,053 2/1951 Parker 313184 2,920,234 1/1960 Luce 313231 2,964,678 12/1960 Reid 313231 3,015,013 12/1961 Laszlo 313-231 JOHN W. HUCKERT, Primary Examiner.

JAMES D. KALLAM, DAVID J. GALVIN, Examiners. 

1. A HIGH INTENSITY RADIANT ENERGY SYSTEM COMPRISING A PRIMARY ARC SOURCE OF RADIANT ENERGY CONSISTING OF A MULTIPLICITY OF ELECTRODES IN A VACUUM CHAMBER, A SECONDARY THERMAL SOURCE OF RADIANT ENERGY, MEANS INTERPOSED THEREBETWEEN TO TRANSFER SAID RADIANT ENERGY FROM SAID SECONDARY THERMAL SOURCE TO SAID PRIMARY SOURCE TO PROVIDE THERMIONIC EMISSION IN SAID PRIMARY ARC SOURCE AND MEANS TO APPLY ALTERNATING CURRENT TO SAID MULTIPLICITY OF ELECTRODES UPON SAID OCCURRENCE OF SAID THERMIONIC EMISSION TO PROVIDE A PLASMA DISCHARGE BETWEEN SAID MULTIPLICITY OF ELECTRODES. 